Optical devices are widely used nowadays. Examples of optical devices are proximity sensors, color sensors, optical encoders or any other similar sensors that comprise an emitter and a receiver for emitting and detecting a radiation. The radiation may be visible or invisible. On some occasions, an optical lens may be coupled to the emitter in order to collimate the radiation to specific directions or distances of interest so that the radiation can be fully utilized for high power efficiency. Similarly, an optical lens may be coupled to the receiver to collimate radiation from a specific direction to the receiver.
For most optical devices that have an emitter and a receiver, the radiation emitted from the emitter is usually directed to an external object or an external medium before being received by the receiver. For optical devices having transmissive arrangement such as transmissive optical encoder, the radiation emitted by the emitter may be transmitted through the external object before being detected by the receiver. For optical devices having reflective arrangement such as proximity sensors and reflective optical encoders, the external object may reflect or redirect a portion of the radiation emitted from the emitter into the receiver.
In response to the radiation detected, the receiver may generate a signal indicative of at least one property of the external object. For example, for proximity sensors, the signal generated by the receiver is indicative of presence of the external object. For color sensors, the signal generated may be indicative of the color of the external object.
However, a portion of the radiation may be detected by the receiver without going through or without being reflected by the external object. The radiation detected by the receiver without being redirected by the external object may be known as crosstalk. Crosstalk is independent from the external object and may reduce the signal to noise ratio of the optical device. Crosstalk may occur within the optical package, or via external structures. For example, most optical devices are to be assembled into an electronic apparatus having a casing. Most casings are transparent but crosstalk may occur due to total internal reflection in which a portion of the radiation emitted by the emitter is reflected into the receiver without going through the external object.
Proximity sensors are sensor devices configured to detect presence of nearby objects without any physical contact. Proximity sensors are commonly used in electronic gears that will turn power-consuming circuitry on or off in response to the proximity sensors detecting something nearby. Use of proximity sensors in such applications may be particularly efficient because they may provide for detecting proximity without having to make physical contact. Proximity sensors may be used in mobile phone, digital photo frames, television, or other electronic devices.